Un nuevo cocodrilo en los depósitos mareales maastrichtianos de la Patagonia Noroccidental

Abstract

This new long-snouted crocodile is characterized by a mandibular symphysis with a single pair of deep ventrolateral sulci, unique among the Crocodylia. If this crocodile is a Dyrosauridae (Mesosuchia),it extends the known geographic range of this family into northem Patagonia. Dyrosaurids are known from Africa, Pakistan, Burma, Portugal, the United States, and northeastem Brazil. The Maastrichtian siliciclastic sequence from northwest Patagonia (Coli Toro Formation) is composed of three main facies: psammitic, heterolithic and pelitic. The facies of sandstones has a tabular to lenticular geometry. Bioturbation is frequent whereas mechanical structures (such as cross bedding, ripples and plane beds) are less frequent. The heterolithic facies is very common and is composed of wavy and lenticular intervals. The pelites are thin and dark. They show carbonized plant debris and veins and crystals of gypsum. Tractional to suspensive tidal processes of deposition are inferred from facies, and sedimentary structures and paleocurrents. Sub to intertidal sand bars and storm bars are suggested for sandstone bodies. The abundance of heterolithic facies in all sections suggests extended intertidal flats, bays or chenier plains surrounded by lowland areas and developed under warm and humid climatic conditions.